For example, as described in Japanese Patent Laid-Open Application No. Hei 7-321184, a processing apparatus is known which forms a new film on the surface of a workpiece or etches previously-laminated films in the fabrication process of a semiconductor device.
This processing apparatus incorporates a process chamber that is made of aluminum or the like. This process chamber is equipped inside with a mounting stage for a workpiece to be mounted on, also serving as a bottom electrode, and a top electrode opposed thereto. In the foregoing processing apparatus, the process chamber is evacuated for depressurization before a workpiece mounted on the mounting stage is controlled to a predetermined temperature while a process gas is blown to its surface to be processed. In this state, high frequencies of, e.g., 60 MHz and 13.56 MHz are respectively applied to the top electrode and the bottom electrode (mounting stage) to produce plasma of the process gas, whereby predetermined etching is applied to the workpiece.
This mounting stage is provided with a cooling jacket, and the workpiece mounted can be cooled down to a desired temperature such as −100° C. Moreover, a plurality of heat transfer gas supply holes are made in the mounting surface of the mounting stage. Then, with the workpiece mounted, a heat transfer gas such as helium (He) that is cooled to a desired temperature is supplied through these heat transfer gas supply holes to improve the efficiency of heat transfer to the workpiece.
Moreover, as disclosed in Japanese Patent Laid-Open Application No. Hei 7-74231, the mounting stage is provided with a plurality of lifter pins which move in vertical directions. When a workpiece is carried in/out, those lifter pins move vertically to facilitate passing the workpiece between the mounting stage and the transportation mechanism. These lifter pins are integrally attached to a single base plate. This base plate moves up and down by being driven by an air cylinder for vertical driving which is attached to the outside of the process chamber through an introduction mechanism.
The aforementioned process chamber, however, incorporates a number of components including metal or non-mental parts such as a focus ring for concentrating plasma, aside from the top and bottom electrodes. Since they gradually wear out at portions exposed to inside the process chamber because of the plasma, these components must be replaced after a lapse of a certain period. Nevertheless, in terms of productivity, their replacement needs to be minimized in frequency for the sake of reducing the period of time and the number of times required for maintenance.
As measures for this, attempts have been made to fabricate the focus ring and other components from materials less prone to wear, such as heavy metal oxides including yttria (Y2O3) and zirconia (ZrO). The fabrication method thereof may involve sintering powder into bulk parts and applying yttria (Y2O3) coating to aluminum-based components. Moreover, the inner surfaces of the process chamber are also given coating to provide portions for suppressing wear resulting from the plasma.
Nevertheless, even if the components are made of heavy metal oxide, the plasma exposure causes slight wear, and fine particles of the heavy metal are often seen suspending in the process chamber.
Besides, other vapors resulting from the plasma suspend around the heavy metal particles. When these vapors are cooled, there occurs the phenomenon that they condense and simultaneously capture heavy metal particles in their proximity, adhering to cooled portions. Since the mounting stage for a workpiece to be mounted on is cooled by the cooling jacket to a low temperature as described above, fine particles containing the heavy metal are deposited on the exposed mounting surface of the mounting stage when no workpiece is mounted thereon.
Then, if a new workpiece is mounted on the mounting stage, the deposited fine particles containing the heavy metal adhere to the underside of the workpiece, giving rise to the problem that the contaminated workpiece is brought out to the subsequent steps.